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package org.daisy.dotify.common.xml;

import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

import javax.xml.XMLConstants;
import javax.xml.namespace.NamespaceContext;

/**
 * Provides a builder for namespace contexts making it easy to provide namespace contexts
 * to for example xpath evaluations.
 * @author Joel Håkansson
 *
 */
public class NamespaceContextBuilder {
	private Map uriForPrefix;
	private Map> prefixesForUri;
	
	/**
	 * Creates a new instance
	 */
	public NamespaceContextBuilder() {
		this(null);
	}
	
	/**
	 * Creates a new instance with the specified default namespace uri
	 * @param defaultNsUri the default namespace uri
	 */
	public NamespaceContextBuilder(String defaultNsUri) {
		uriForPrefix = new HashMap<>();
		prefixesForUri = new HashMap<>();
		add(XMLConstants.DEFAULT_NS_PREFIX, defaultNsUri==null?XMLConstants.NULL_NS_URI:defaultNsUri);
	}
		
	/**
	 * Adds a new namespace binding with the specified prefix and uri
	 * @param prefix the namespace prefix
	 * @param uri the namespace uri
	 * @return returns this builder
	 */
	public NamespaceContextBuilder add(String prefix, String uri) {
		if (uriForPrefix.put(prefix, uri)!=null) {
			throw new IllegalArgumentException("Prefix already bound: " + prefix);
		};
		Set prefixes = prefixesForUri.get(uri);
		if (prefixes==null) {
			prefixesForUri.put(uri, new HashSet<>(Arrays.asList(new String[]{prefix})));
		} else {
			prefixes.add(prefix);
		}
		return this;
	}
	
	/**
	 * Creates a new namespace context with the currently configured settings
	 * @return returns a new namepsace context
	 */
	public NamespaceContext build() {
		return new NamespaceContextImpl(this);
	}
	
	private static class NamespaceContextImpl implements NamespaceContext {
		private final Map uriForPrefix;
		private final Map> prefixesForUri;
		
		private NamespaceContextImpl(NamespaceContextBuilder builder) {
			this.uriForPrefix = new HashMap<>(builder.uriForPrefix);
			this.prefixesForUri = new HashMap<>(builder.prefixesForUri);
		}

		@Override
		public String getNamespaceURI(String prefix) {
			throwExceptionIfNull(prefix);
			switch (prefix) {
				case XMLConstants.XML_NS_PREFIX: return XMLConstants.XML_NS_URI;
				case XMLConstants.XMLNS_ATTRIBUTE: return XMLConstants.XMLNS_ATTRIBUTE_NS_URI;
				default:
					return withDefault(uriForPrefix.get(prefix), XMLConstants.NULL_NS_URI);
			}
		}

		@Override
		public String getPrefix(String namespaceURI) {
			throwExceptionIfNull(namespaceURI);
			switch (namespaceURI) {
				case XMLConstants.XML_NS_URI: return XMLConstants.XML_NS_PREFIX;
				case XMLConstants.XMLNS_ATTRIBUTE_NS_URI: return XMLConstants.XMLNS_ATTRIBUTE;
				default:
					return getFirstMatchOrNull(prefixesForUri.get(namespaceURI));
			}
		}

		@Override
		public Iterator getPrefixes(String namespaceURI) {
			throwExceptionIfNull(namespaceURI);
			switch (namespaceURI) {
				case XMLConstants.XML_NS_URI: return toIterator(XMLConstants.XML_NS_PREFIX);
				case XMLConstants.XMLNS_ATTRIBUTE_NS_URI: return toIterator(XMLConstants.XMLNS_ATTRIBUTE);
				default:
					return toUnmodifiableIterator(prefixesForUri.get(namespaceURI));
			}
		}
		
		private static void throwExceptionIfNull(String value) {
			if (value==null) {
				throw new IllegalArgumentException("Null not allowed.");
			}
		}
		
		private static  T withDefault(T value, T def) {
			return (value==null)?def:value;
		}
		
		private static  T getFirstMatchOrNull(Set set) {
			if (set!=null && !set.isEmpty()) {
				return set.iterator().next();
			} else {
				return null;
			}
		}
		
		private static  Iterator toUnmodifiableIterator(Set set) {
			if (set!=null && !set.isEmpty()) {
				return Collections.unmodifiableSet(set).iterator();
			} else {
				return Collections.emptyListIterator();
			}
		}
		
	    @SafeVarargs
		private static  Iterator toIterator(T ... value) {
			return Arrays.asList(value).iterator();
		}

	}
}